This study investigated the effectiveness of underlining while reading in readers' understanding of textual information.We researched from the two points, which were difficulties of texts and length of reading time.Subjects were assigned to three groups as follows: (1) Underlining group; they were instructed to read the text and they could underline the text wherever they wanted, (2) Prompting group; they were instructed to read the prompted text but they could't underline themselves, and (3) Control group; they were instructed to read the text which had no line and they couldn't underline themselves.The results showed that the prompting improved the subjects' recall of the underlined imformation regardless of the texts' difficulties or the length of reading time.Underlining,however,was effective only when the texts were difficult and subjects were given enough reading time.Besides that, important imformation such as key words was apt to be recalled even if there was not underlined.